1. In a heavy 4- to 5-quart saucepan, bring 2 quarts of water to a boil over high heat. Drop in the chilies and boil, uncovered, for 5 minutes, then drain them thoroughly and run cold water over them.
2. Split the chilies in half and remove the seeds. Combine the chilies, oil, vinegar and salt in the jar of a blender, and blend them at high speed until the mixture is reduced to a smooth, thick puree.
3. To make the sauce by hand, puree the chilies in a food mill set over a bowl. Stir in the oil, vinegar and salt.
4. This sauce is used as a substitute for fresh mild chili, and can be kept, covered and refrigerated, for about 2 weeks, although the flavor will diminish as the sauce stands.
